[Ed]

EP-

Definitely dig out the foam now and replace it with new foam. That foam is at least 25 years old.

You can buy the foam (2-part mixture) and pour it in place. Just be sure you do a little bit at a time and leave room (or escape holes) so that the excess foam has a place to leech out when it expands beyond the capacity of the cavity you are pouring the foam into.

Or, like John R. said, you can take the boat to a fiberglass shop and see if they will do it for you. Some shops use a foam gun to blow it in and others use the process I mentioned above.

Be sure to wear gloves!